Integrated cracking-alkylation process



H. J. HEPF INTEGRATED CRACKING-ALKYLATION PROCESS Filed Dc. 14, 1955 Dec. 10,1957

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D Q o /SOBU TA/VE CONVERS/N, PER CE N 7' K I BY w United States Patent() INTEGRATED CRACKlNG-ALKYLATION PROCESS Harold I. Hepp, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of' Delaware Application December 14, 1953, Serial No. 397,899

3 Claims. (Cl. 26o-683.4)

This invention relates to the manufacture of hydrocarbons. In one aspect this invention relates to the manufacture of motor fuels. In one aspect this invention relates to the manufacture of olefins by reacting isobutane under selected conditions of pressure, temperature and per-pass conversion. In another aspect this invention relates to an integrated cracking-alkylation process wherein isobutane is cracked under specified conditions for producing eluent containing isobutane, propylene and butylene, in predetermined proportions, and, wherein said effluent is de-ethanized and then charged, subsequent to depentanization, if desired, as sole feed to an alkylation system and converted therein to hydrocarbons boiling in the gasoline range. In another aspect this invention relates to a process for cracking isobutane under pressure conditions to produce propylene and butylene in high ultimate yield and in a ratio to unreacted isobutane in the eluent such that the resulting eflluent freed of materials lighter than propylene can be charged as sole feed to an alkylation system for conversion to motor fuel.

In accordance with this invention, isobutane is subjected to conversion at a pressure above about 80 p. s. i. g., so as to produce propylene and butylene in high ultimate yields, under which conditions total ellluent can be produced containing isobutane, propylene and butylene in relative mol ratios such that resulting demethanized or de-ethanize'd conversion effluent is particularly applicable as sole feed to an alkylation system for conversion to isoparatiins boiling in the gasoline range. In accordance with one concept of this invention, total eluent from the above-described conversion is eiiiciently fractionated at its existing pressure to remove C2 hydrocarbons and lighter materials therefrom (de-ethanization) and the resulting residual eluent is charged as sole feed, subsequent to depentanization, if desired, to an alkylation system and therein converted to isoparaflins boiling in the gasoline range.

Temperatures employed, in the conversion of isobutane to olefms in accordance with this invention are generally Within the range of 1l00-1400 F., although temperatures outside that range can be employed. More generally preferred temperatures are within the range of 1200-1350 F.

Pressures employed are those above 80 p. s. i. g., generally within 12S-500 p. s. i. g., a still narrower range of about 150-300 p. s. i. g. being preferred because higher ultimate yields of olefin are obtained under these conditions, and relative ratios of isobutane, propylene and butylenes are obtained, which are especially suitable such that de-ethanized eluent can be advantageously charged as sole feed for conversion, by alkylation, to gasoline boiling-range hydrocarbons.

Time conditions employed are generally from about 0.03 to 150 seconds for a per-pass conversion of isobutane of from -70 mol percent at 1100 to 1400 F. and 125 to 500 p. s. i. g., and from about 0.2 to 12 seconds for a per-pass conversion of isobutane of from 25 to 55-mo1 percent at 1200 to 135o F. and 150 to 30o p.'s. i. gi

the range 150-300 p.

2,816,150 Patented Dec. l0, 1957 rzCe This latter range of 25 to 55 mol percent per-pass conversion of isobutane provides high ultimate yields of propylene and butylene, and also suitable relative ratios of isobutane, propylene and butylene are obtained as sole feed to alkylation for conversion to motor fuels. The conditions of time, temperature and pressure must be correlated so as .to give the desired per-pass conversion of isobutane.

When it is desired to carry out the integrated crackingalkylation process of this invention, isobutane cracking is regulated so as to provide de-ethanized eluent containing isobutane in a mol ratio to olens (after deethanization) in the range of about 1:1 to 10:1, more preferably from 4:1 to 6:1, under which conditions the said de-ethanized eflluent can be charged as sole feed to alkylation for conversion to high quality motor fuels. The cracking operations required for achieving the abovedescribed ranges of isobutane to olefin ratios are also those providing for highest ultimate yields of propylene and butylene. Isoparains other than isobutane give high yields of ethylene. Therefore, isobutane is the only possible feed for this process.

Although inl carrying out the integrated cracking- Ialkylation process, the eluent from isobutane cracking is preferably de-ethanized and often advantageously depentanized prior to charging same as sole feed to alkylation, neither of these steps is required. Thus, the said eflluent can be demethanized, and ethylene in the feed to alkylation can be utilized as an alkylating reactant, as for example when employing a 2stage alkylation step. in the rst of which steps ethyleneis not converted, but is reacted with isoparafins in the latter. The presence in the alkylation feed of any pentane and heavier hydrocarbon materials produced in the cracking process of the integrated cracking-alkylation process herein, is not generally desirable because of the effect of diolelins on catalyst consumption, i. e., to increase catalyst consumption to an unduly high rate, particularly when hydrotluoric acid or sulfuric acid are employed as catalysts.

A further advantage of my invention is provided with reference to preparation of total isobutane cracking effluent for alkylation. Because the cracking of isobutane is maintained at a pressure above about p. s. i. g., generally from 12S-500 p. s. i; g., the etiiuent from isobutane cracking can be etliciently fractionated for removal of materials lighter than propylene and to effect depentanization, without the need for pressurization, such pressures, particularly those exceeding p. s. i. g. being Iadvantageously employed in the removal of C2 and lighter materials from cracking eluent. The elimination of the need for pressurization to separate C2 and lighter materials, and to depentanize, provides a considerable saving in equipment and manpower requirements and thereby facilitates operation from the viewpoint of economics, thus adding to the economic feasibility of the process of this invention.

The invention is illustrated with reference to the drawing of Figure 1, which is a diagrammatic ilow sheet illustrating one manner in which process of this invention can be carried out.

Figures 2, 3 and 4 are plots of curves setting forth data illustrative of process of this invention.

With reference to Figure l, isobutane, or an isobutanecontaining stream is passed via lines 10 and 10' to isobutane-cracking zone 14, as for example, a Selas furnace. Isobutane, as feed in any desired proportion, can also be introduced via line 15 into line 10 from a normal butane isomerization zone 13, described hereinafter. Preferred isobutane-cracking conditions in zone 14, described hereinabove, are generally employed, namely a pressure .in s. i. g., a temperature in thek range of about 1200-1350 F., and time conditions providing 3 for 25h-55 mol percent isobutane cracking, i. e., per-pass conversion. Efuent is withdrawn from zone 14 via` line 17 at the existing pressure inzone 14 and introduced into separation zone 18, comprising any desired arrangement of fractional distillation equipment; although, it?v desired, other separation means may be' employed in zone 128'. In1 zone 18 eluent from zone 14"is1de'etha`niz'ed, and the C2 and lighter materials,` principally etliane'; ethylene,- methane and hydrogen, are withdrawn via1in`e"19.- Heavy ends (pentanes and heavier) are" withdrawn via lineV 20,- and eiuent fromseparation zonel 18, in line 21E, constitutes unreacted isobutane from zone 14 together with propylene and butylene' formed therein. Ellluent from zone 18, in line 21, contains` isobutane', proplyerie butylene in relative ratios suitable for charging'- the last: said eiuent as sole feed to an' alkylationsystem for conversion to hydrocarbons boiling in the gasoline range', andis passed to alkylation zone`r 22, preferably an HF- alkylation unit, and therein converted to' hydrocarbons boilingl in the gasoline range, i. e., by alkylation of isobutane with propylene and/or butylene.

The following conditionsare exemplary of thosel eni' ployed in conducting alkylation in' zone 22, when e1rlp`l yA ing HF as the alkylation catalyst.

Broad Preferred Range Range Temperature, F E11-150 751100' Pressure-.'...-r... r() l" Isoparaiu/Olen, Mol ra o.- 3 1-`tov1021 4:,1 @10:1- Hydrocarbon/HF, vol: ratio.. 4:1 to 1:4 1%:1' to 1:1145 A cld Composition, HF, wt. p cen 85-95 90195y Contact time, Minutes.. 5-25 10-15 1 Sutilcleut to keep' reactants lluuld.

Total etlluent from alkylation zone 22 is passed via line 24 to product 'separation means 25 comprising any desirable means for separating hydrouorie acid and hy drocarbon phases, and for then fractionating hydrocarbon phase into desired alkylation products and lighter hydrocarbons. C3 and lighter materials separated in Zone 25 are withdrawn via line 26; a C5 and heavier hydrocarbon fraction, well-balanced for use as motor fuel, particularly with reference to distillation range (distribution) volatility and octane number, is withdrawn via line 27; isobutane unreacted in zone 22 is withdrawn via line 1-6, and any normal butane present is withdrawn via line 12 or 12 or both. Isobutane in line 16, present as 'a result of in situ build-up of isobutane in zone 22 lcan be recycled if desired via line to zone 14, and/or via line 23 to HF alkylation zone 22. Normal butane in line A12 can be withdrawn to storage by way of line 12 or passed together with normal butane from any outside "source, if the latter is desired, to normal butane isomerization zone 13 and therein converted to isobutane which can then be charged to isobutane cracking zone 14 via lines 15 and 10".

Normal butane isomerization conducted in Vzone 13 can be in accordance with any method known in the art for isomerizing normal butane to isobutane such as for example, isomerization in the presence of aluminum chloride as a catalyst.

Any known alkylation catalyst can be employed in zone 22, although as stated hereinabove it is preferred to use concentrated hydrouoric acid or concentrated sulfuric lacid as van alkylation catalyst. Among such alkylation catalysts that can also be employed in zone 22 are aluminum and zinc chlorides and bromides, mixed salts of aluminum chloride or bromide with various metal chlorides and bromides, such as an equimolar mixture of sodium and aluminum chlorides, boron fluoride, zirconium iuride and the like. However, of these catalysts, sulfuric acid and concentrated hydrofloric acid are preferred, because they appear to promote the union of propylene and butylenes with isobutane more selectively vthan other known alkylation catalysts.

Data in the following tabulation show that, unexpectedly when cracking isobutane-at elevated pressuresin-ac cordance with the present invention, yield of olen is not substantially adversely affected.

Thus, in Table I are shown data obtained from cracking isobutane, demonstrating that no appreciable loss in olen yield results from increasing the pressure of isobutane cracking from atmospheric to 200 p. s. i. g. at a given temperature and conversion level; the said tabulation' also showing that at a given pressure `and conversion, an increase in temperature Within the cracking temperature' range of this invention results in an increase in olen yield.

TABLE I Eect of temperature Pressure, p. s. i. g 200 200 200 Temperature, F 1, 200 1, 250 1, 300 Percent Conversion 50V 50 50 Eect of pressure Pressure, p. s. i. g 0 200 100 300 Temperature, F.,- 1, 200 1, 200 I, 250 1, 250 1, 250 Percent', Conversion.l 50 50 50 50 50l o'iaan Yara, 1bn/roo ns; to'.

reacted:

OsHs 27. 2 24. 6 24. 7 25. 1 30.3 04m.; A ars d 31. 5 39. Q 39. 2 l 3s. 6

Total 65.0 62 1 64 6 65.3 68 9 Data obtained from isobutane cracking under process conditions of this invention are illustrated by way of the product yield curves, which show the olefin yields obtained at various conversion levels, at 1250 F. and 300 p. s. g. (Figure 2) and at 1300o F. and 200 p. s. i. g. (Figure 3). y

The conversion levels required to give an isobutane cracking effluent stream containing isobutane, propylene and butylenes in relative proportions suitable for being directly charged as sole feed to the alkylation system are also the conversion levels at which ultimate yields of olen are the highest.

Data obtained from cracking isobutane at 1250 F. and at 200 p. s. i. g., showing Yproplyene and butylene yields at various conversion levels are tabulated in Table II and plotted in Figure 4.

TABLE II Conversion vf isobumnear 1250" and 200 p. S. 11g., Mols/ mols In Table III and Figure 4 are data showing mol ratios of isobutane to olefin (propyleue-l-butylene) obtained at various conversion levels when cracking isobutane at 1250 F. and 200 p. `s. i.

TABLE In Mol ratio i-C4 to olefin (propylene-l-butylene) at indicated conversion of isobutane Mol Ratio Percent Conversion i-C4 to olefin Table IV is illustrative of product distribution of isobutane cracking in accordance with this invention at different conversion levels, particularly illustrating high propylene and butylene yields obtained over a broad range of conversions.

MOLS PRODUCT/100 MOLS ISOBUTANE CONVERTED Hydrogen 30. 5 42. 0 Methane 65. 4 56. 1 Ethylene... 10. 9 6. 3 Ethane-.. 3. 4 0. 8 Propylen 35, 1 46. 7 Propane.- 7. 4 4. 7 Butylene 37. 8 42. 8 Pentanes and heavier 4. 8 0. 6

Reasonable variation and modication are possible within the scope of the foregoing disclosure, drawings, and appended claims to the invention, the essence of which is that a process is provided for reacting isobutane ata pressure above about 80 p. s. i. g., generally from 125- 500 p. s. i. g., so as to produce propylene and butylene in high ultimate yield under which conditions tota-l eifluent can be produced, which, subsequent to demethanization or de-ethanization, and depentanization when desired, is particularly applicable as sole feed to an alkylation system for conversion to isoparain hydrocarbons boiling in the gasoline range; in accordance with another concept, this invention providing for effecting the above-said deethanization at the substantially existing conversion pressure, thus eliminating necessity for pressurization to eilect de-ethanization, and depentanization when desired; in accordance with another concept, this invention providing an inetgrated isobutane cracking-alkylation process, in which demethanized or de-ethanized effluent from isobutane cracking is charged, subsequent to depentanization, if desired, as sole feed to an alkylation system, preferably HF-alkylation, and converted therein to isoparains boiling in the gasoline range to form high quality motor fuels.

I claim:

1. An integrated cracking-alkylation process comprising passing isobutane into a cracking zone maintained at a temperature within the range of 1200-1350 F., under a pressure in the range of -300 p. s. i. g., for a period of time within the range of 0.2 to l2 seconds so as to maintain a per-pass conversion of isobutane Within the range of 25-55 mol percent and thereby providing a total cracking effluent containing isobutane in a mol ratio to propylene plus butylene suitable for charging as the sole feed to an alkylation zone; passing total eluent from said cracking zone under substantially cracking pressure into a separation zone and therein separating, under said pressure, ethane and lighter materials, from said effluent; passing resulting de-ethanized effluent from said separation zone as sole feed to an alkylation zone and therein reacting same under alkylating conditions to produce normally liquid hydrocarbons boiling in the gasoline range, and recovering normally liquid hydrocarbons so produced as product of the process.

2. An integrated cracking-alkylation process comprising cracking isobutane at a temperature Within the range of 1200-1350 F., at a pressure in the range of 150-300 p. s. i. g., for a period of time within the range of 0.2 to 12 seconds so as to (l) effect a per-pass conversion of isobutane of from 25-55 mol percent and (2) to provide total cracking effluent containing isobutane in a mol ratio to propylene plus butylene suitable for charging to an alkylation zone as the sole feed; passing total effluent from said cracking under substantially cracking pressure into a separation zone and therein separating, under said pressure, ethane and lighter materials and pentane and heavier materials from said total elluent; passing resulting deethanized and depentanized total eiiluent from said separation zone as sole feed to an alkylation zone and therein maintaining same in contact with liquid hydrofluoric acid under alkylating conditions to react isobutane with propylene and butylene to produce a motor fuel, and recovering motor fuel so produced.

3. An integrated cracking-alkylation process comprising passing isobutane into a cracking zone maintained at a temperature within the range of 1200-1350" F., under a pressure in the range of 150-300 p. s. i. g., for a period of time within the range of 0.2 to 12 seconds so as to (l) maintain a per-pass conversion of isobutane within the range of 25-55 mol percent and (2) to provide total cracking eiiuent containing isobutane in a mol ratio to propylene plus butylene suitable for charging as the sole feed to an alkylation zone; passing total eilluent from said cracking zone under substantially cracking pressure into a separation zone and therein separating under said pressure, ethane and lighter materials from said eiluent; passing resulting de-ethanized etlluent from said separation zone as sole feed to an alkylation zone and therein reacting same under alkylating conditions to produce normally liquid hydrocarbons boiling in the gasoline range, recovering isobutane from eluent from said alkylation zone and recycling same to said cracking zone, and recovering normally liquid product from said alkylation zone.

References Cited in the tile of this patent UNITED STATES PATENTS 2,312,539 Frey Mar. 2, 1943 2,336,005 Frey Dec. 7, 1943 2,417,875 Leonard Mar. 25, 1947 2,428,417 Gary Oct. 7, 1947 2,460,303 McAllister et al. Feb. 1, 1949 

1. AN INTEGRATED CRACKING-ALKYLATION PROCESS COMPRISES ING PASSING ISOBUTANE INTO A CRACKING ZONE MAINTAINED AT A TEMPERATURE WITHIN THE RANGE OF 1200-1350*F., UNDER A PRESSURE IN THE RANGE OF 150-300 P.S.I.G., FOR A PERIOD OF TIME WITHIN THE RANGE OF 0.2 TO 12 SECONDS SO AS TO MAINTAIN A PER-PASS CONVERSION OF ISOBUTANE WITHIN THE RANGE OF 25-55 MOL PERCENT AND THEREBY PROVIDING A TOTAL CRACKING EFFLUENT CONTAINING ISOBUTANE IN A MOL RATIO TO PROPYLENE PLUS BUTYLENE SUITABLE FOR CHANGING AS THE SOLE FEED TO AN ALKYLATION ZONE; PASSING TOTAL EFFULENT FROM SAID CRACKING ZONE UNDER SUBSTANTIALLY CRACKING PRESSURE INTO A SEPARATION ZONE AND THEREIN SEPARATING UNDER SAID PRESSURE, ETHANE AND LIGHTER MATERIALS, FROM SAID EFFLUENT; PASSING RESULTING DE-ETHANIZED EFFLUENT FROM SAID SEPARATION ZONE AS SOLE FEED TO AN ALKYLATION ZONE AND THEREIN REACTING SAME UNDER ALKYLATING CONDITIONS TO PRODUCE NORMALLY LIQUID HYDROCARBONS BOILING IN THE GASOLINE RANGE, AND RECOVERING NORMALLY LIQUID HYDROCARBONS SO PRODUCED AS PRODUCT OF THE PROCESS. 